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01-13-2019, 07:34 PM - 1 Like   #46
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QuoteOriginally posted by Paul the Sunman Quote
I have 14 Pentax lenses. No "bad copies" yet, though the DA 16-85 did lose a screw and need fixing.
People claim I've lost a few screws, and can't be fixed.

01-13-2019, 07:55 PM   #47
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QuoteOriginally posted by normhead Quote
People claim I've lost a few screws, and can't be fixed.
No comment.
01-14-2019, 05:15 PM   #48
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From what I've seen on these forums, another plus for the DA 18-135mm is a bad copy seems to be more rare than most other zoom lenses in this class of lens. Definitely more rare than the DA 16-85mm.

As far as wide open aperture, this also depends on what is being photographed. The lens is capable of f/4.5 up to 70mm, at which Imaging Resource shows only 17% of the frame being under 2 blur units- so a "bad" setting. I'm with the skeptical view expressed by UncleVanya, in that I've not seen many if any lens displaying comparatively good sharpness at f/16, and also it is very unlikely for sharpness to fall in mid-FL then pick up drastically at the longest FL. All other tests of this lens indicate progressive loss of edge performance as it is zoomed to its longest FL, which is the usual thing expected of any zoom lens. I say, use your eyes and look at the still life image provided by Imaging Resource. Unfortunately, a shot at or near 70mm is not given, just 18, 50, and 135mmm, wide pen and at f/8. I would say the 135mm results wide open represents what to expect at its worst.

It seems very odd to me that they show a drop to only 16% at 100mm and f/5.6, but coming back up to 28% when continuing to zoom to 135mm! This is out of sync with what usually happens and at odds with other tests.

What is consistent between test reports, is the lens loses edge sharpness at longer zoom settings, but central performance remains very good to excellent. So even at its worst, when shooting a central subject, as in portrait, the subject will still be sharp, though the outer area is not.

Last edited by mikesbike; 01-14-2019 at 05:21 PM.
01-14-2019, 07:36 PM   #49
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QuoteOriginally posted by mikesbike Quote
I would say the 135mm results wide open represents what to expect at its worst.
Just to clarify, in case this is taken out of context: in terms of the % of the image that is sharp, yes, 135mm wide open has the lowest. But even wide open at 135mm the centre part of the image is still sharp (as you emphasize later in the post). And that's usually what matters most.

In my experience, the weakest performance for the lens is wide open (f3.5) at 18mm, because it isn't really sharp anywhere. Fortunately that's not a setting that I have found much need for. Stopped down to f6.3 or f8 at 18mm is fine.

01-15-2019, 07:11 AM   #50
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QuoteOriginally posted by mikesbike Quote
What is consistent between test reports, is the lens loses edge sharpness at longer zoom settings, but central performance remains very good to excellent. So even at its worst, when shooting a central subject, as in portrait, the subject will still be sharp, though the outer area is not.
And what's apparent in my own use, is it's just a really useful lens. What people seem to be missing is that at 135mm, the centre is almost as sharp as the DA*60-250 or DA*200. I know there are people who will argue that they can't work with that. That changes my use not one little bit. The question for me is simply is 135mm with soft edges better than no 135mm at all. The lens has excellent sharpness at ƒ5.6 throughout it's entire range. That's a tool I can use.

If others for some reason can't, I'm OK with that.
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